Interlock mechanism

ABSTRACT

An interlock mechanism for a power tool releasably coupled first ( 10 ) and second ( 40 ) portions. The mechanism includes a spring ( 202 ) normally biased to a first position in which it is closed and an actuator ( 208 ) enabling the spring to be moved to a second position in which it is open. The actuator has a spring-engaging surface ( 216 ) formed from several individual surfaces which are non coplanar.

[0001] The present invention relates to an interlock mechanism and hasparticular relevance to such an interlock mechanism as used on acomposite power tool formed from a body able to accept and one of aplurality of interchangeable heads. Each one of the heads may couplewith the body to provide a power tool capable of achieving a dedicatedtask determined by the head.

[0002] In EP-A-899,063 there is shown a power tool system formed from acommon body and a plurality of tool heads, each of which is selectivelymountable on the body. Each head is designed to achieve a differentfunction, such as drilling, sanding or sawing.

[0003] The manner in which the heads attach to the body is important.The coupling must be firm enough to permit efficient transmission oftorque from the body to the head. However, the coupling also needs to becapable of being released easily by a user of the tool which wishes tochange the head for another head in order to achieve a different tooloperation.

[0004] Whilst the interlock mechanism described in the above patentapplication functions satisfactorily, release of the mechanism had thepotential to be problematical as the user had no way of knowing when thecoupling had been broken and hence the tool head was free to be removedfrom the tool body.

[0005] It is an object of the present invention to provide an interlockmechanism which at least alleviates the above shortcomings by provisionof an interlock mechanism which provides the user with a positiveindication of when the mechanism is released.

[0006] According to the present invention there is provided interlockmechanism for releasably coupling first and second portions of a powertool comprising: a spring normally biassed to a first, closed position;and an actuator co-operable with the spring to urge the spring, underinfluence of the actuator, into a second, open position, the interlockmechanism characterised by the actuator having a spring-engaging surfaceformed from a plurality of individual surfaces which are not coplanar.Provision of the spring-engaging surface with a plurality of individualnon-coplanar surfaces enables the interlock mechanism to give a positiveindication of being open, rather than the hitherto-known mechanism whichemploys a linear-style release mechanism which gives the user theindication of the state of operation of the interlock.

[0007] In a preferred embodiment the spring-engaging surface defines adual-gradient structure. Providing a structure with a dual-gradientallows for non-linear movement of the spring between the first, openposition and the second, closed position. This means that when the useroperates the actuator different rates of movement of the spring betweenthe open and closed positions are possible with the same rate ofmovement of the actuator dependent upon which gradient of thedual-gradient surface the spring is engaged with.

[0008] Additionally or alternatively the spring is formed as a U-shapedmember, the open arms of which are co-operable with the actuator. Thisstructure enables an attachment to be coupled by the interlock mechanismby passing between the open arms and being clasped thereby.

[0009] Preferably the open arms of the spring contact thespring-engaging surface of the actuator such that movement of theactuator causes concomitant movement of the arms of the spring. Thisallows the user of the mechanism to activate it simply by operating onthe actuator. Preferably the arms of the U-shaped member are notstraight.

[0010] Advantageously the actuator defines a seat within which at leasta portion of the spring sits, the seat including a plurality of parallelmembers arranged to engage with the at least portion of the spring,thereby to retain the spring in the seat in the first, closed position.This allows the spring to be held in its first, open position by theactuator and hence ready for coupling with an attachment presented tothe interlock mechanism without the need for movement of the spring.

[0011] Preferably the plurality of parallel members comprise twoprojections, each of which projections engages with a corresponding oneof the open arms of the U-shaped member. Preferably the actuator has aplurality of spring-engaging surfaces. Also each of the arms of theU-shaped member engages with a respective one of the plurality ofspring-engaging surfaces.

[0012] A preferred embodiment to the present invention will now bedescribed, by way of example only, with reference to the accompanyingillustrative drawings in which:

[0013]FIG. 1 shows a front perspective view of a body portion of a powertool in accordance with the present invention;

[0014]FIG. 2 shows a side elevation of the power tool of FIG. 1 with adrill head attachment;

[0015]FIG. 2a shows a part side elevation of the power tool of FIG. 2having one half of the clam shell of the tool body and tool headremoved;

[0016]FIG. 3 shows a side elevation of the power tool of FIG. 1 with ajigsaw head attachment;

[0017]FIG. 4 shows a side elevation of the tool body of FIG. 1;

[0018]FIG. 5a shows a side elevation of the body portion of the powertool of FIG. 1 with one half clam shell removed;

[0019]FIG. 5b shows the front perspective view of the body portion ofFIG. 1 with half the clam shell removed;

[0020]FIG. 6 is a front elevation of the power tool body of FIG. 1 withpart of the clam shell removed;

[0021]FIG. 7a is a perspective view of the tool head release button;

[0022]FIG. 7b is a cross-section of the button of FIG. 7a along thelines 7-7;

[0023]FIG. 7c is a front view of a tool head clamping spring for thepower tool of FIG. 1;

[0024]FIG. 8 is a side elevation of the drill head of FIG. 2;

[0025]FIG. 8a shows a cross-sectional view of a cylindrical spigot (96)of a tool head taken along the lines of VIII-VIII of FIG. 8;

[0026]FIG. 8b is a view from below of the interface (90) of the drillhead tool attachment (40) of FIG. 8;

[0027]FIG. 9 is a rear view of the drill head of FIG. 8;

[0028]FIG. 10a is a rear perspective view of the jigsaw head of FIG. 3;

[0029]FIG. 10b is a side elevation of the jigsaw tool head of FIG. 3with half clam shell removed;

[0030]FIG. 10c is a perspective view of an actuating member from below;

[0031]FIG. 10d is a perspective view of the actuating member of FIG. 10cfrom above;

[0032]FIG. 10e is a schematic view of a motion conversation mechanism ofthe tool head of FIG. 10b.

[0033]FIG. 11 is a front elevation of the combined gearbox and motor ofthe power tool of FIG. 1;

[0034]FIG. 12 is a schematic cross-sectional view of the motor andgearbox mechanism of FIG. 11 along the lines XI-XI;

[0035]FIG. 13 is a side elevation of the drill head as shown in FIG. 8with part clam shell removed.

[0036] Referring now to FIG. 1, a power tool shown generally as (10)comprises a main body portion (12) conventionally formed from two halvesof a plastics clam shell (14, 16). The two halves of the clam shell arefitted together to encapsulate the internal mechanism of the power tool,to be described later.

[0037] The body portion (10) defines a substantially D-shaped body, ofwhich a rear portion (18) defines a conventional pistol grip handle tobe grasped by the user. Projecting inwardly of this rear portion (20) isan actuating trigger (22) which is operable by the user's index fingerin a manner conventional to the design of power tools. Since such apistol grip design is conventional, it will not be described further inreference to this embodiment.

[0038] The front portion (23) of the D-shaped body serves a dual purposein providing a guard for the user's hand when gripping the pistol gripportion (18) but also serves to accommodate battery terminals (25) (FIG.5a) and for receiving a battery (24) in a conventional manner.

[0039] Referring to FIGS. 5a and 5 b, the front portion (23) of the bodycontains two conventional battery terminals (25) for co-operatingengagement with corresponding terminals (not shown) on a conventionalbattery pack stem (32). The front portion (23) of the body issubstantially hollow to receive the stem (30) of the battery (24) (asshown in FIG. 5) whereby the main body portion (33) of the batteryprojects externally of the tool clam shell. In this manner, the mainbody (33) of the battery is substantially rectangular and is partiallyreceived within a skirt portion (34) of the power tool clam shell forthe battery to sit against and co-operate with an internal shoulder (35)of the power tool in a conventional manner.

[0040] The battery has two catches (36) on opposed sides thereof whichinclude (not shown) two conventional projections for snap fittingengagement with corresponding recesses on the inner walls of the skirt(34) of the power tool. These catches are resiliently biassed outwardlyof the battery (32) so as to effect such snap engagement. However, thesecatches may be displaced against their biassing to be moved out ofengagement with recesses on the skirt to allow the battery to be removedas required by the end user. Such battery clips are again consideredconventional in the field of power tools and as such will not bedescribed further herein.

[0041] The rear portion (18) of the clam shell has a slightly recessedgrip area (38) which recess is moulded in the two clam shell halves. Toassist comfort of the power tool user, a resilient rubberised materialis then integrally moulded into such recesses to provide a cushionedgrip member. This helps provide a degree of damping of the power toolvibration (in use) against the user's hand.

[0042] Referring to FIGS. 2 and 3, interchangeable tool heads (40, 42)may be releasably engaged with the power tool body portion (12). FIG. 2shows the power tool (10) whereby a drill head member (40) has beenconnected to the main body portion (12) and FIG. 3 shows a jigsaw headmember (42) attached to the body portion (12) to produce a jigsaw powertool. The mechanisms governing the attachment orientation andarrangement of the tool heads on the tool body will be described later.

[0043] Referring again to FIGS. 5a and 5 b, which shows the power tool(10) having one of the clam shells (16) removed to show, schematically,the internal workings of the power tool. The tool (12) comprises aconventional electrical motor (44) retainably mounted by internal ribs(46) of the clam shell (14). (The removed clam shell (16) hascorresponding ribs to also encompass and retain motor). The outputspindle (47) of the motor (FIG. 12) engages directly with a conventionalepicyclic gearbox (also known as a sun and planet gear reductionmechanism) illustrated generally as (48) (reference also made to FIG.11). To those skilled in the art, the use of an epicyclic gear reductionmechanism is standard practice and will not be described in detail heresave to explain that the motor output generally employed by such powertools will have a rotary output of approximately 15,000 rpm whereby thegear and planetary reduction mechanism will reduce the rotational speedof the drive mechanism dependent on the exact geometry and size of therespective gear wheels within the gear mechanism. However, conventionalgear reduction mechanisms of this type will generally used to employ agear reduction of between 2 to 1 and 5 to 1 (e.g. reducing a 15,000 rpmmotor output to a secondary output of approximately 3,000 rpm). Theoutput (49) of the gear reduction mechanism (48) comprises an outputspindle, coaxial with the rotary output axis of the motor, and has amale cog (50) again mounted coaxially on the spindle (49).

[0044] The male cog (50) shown clearly in FIG. 5b comprises sixprojecting teeth disposed symmetrically about the axis of the spindle(49) wherein each of the teeth, towards the remote end of the cog (50),has chamfered cam lead-in surfaces tapering inwardly towards the axis tomate with co-operating cam surfaces on a female cog member having sixchannels for receiving the teeth in co-operating engagement.

[0045] Referring to FIGS. 1, 5a, 5 b and 6, the power tool body portion(12) has a front facing recess (52) having an inner surface (54)recessed inwardly of the peripheral edge of a skirt (56) formed by thetwo halves of the clam shell. Thus the skirt (56) and the recessedsurface (54) form a substantially rectangular recess on the tool bodysubstantially co-axial with the motor axis (51). The surface (54)further comprises a substantially circular aperture (60) through whichthe male cog (50) of the gear mechanism projects outwardly into therecess (52). As will be described later, each of the tool heads whenengaged with the body will have a co-operating female cog for meshedengagement with the male cog.

[0046] As is conventional for modern power tools, the motor (44) isprovided with a forward/reverse switch (62) which, on operation,facilitates reversal of the terminal connections between the battery(24) and the motor (44) via a conventional switching arrangement (64),thereby reversing the direction of rotation of the motor output asdesired by the user. As is conventional, the reverse switch (62)comprises a plastics member projecting transversely (with regard to theaxis of the motor) through the body of the tool so as to project fromopposed apertures in each of the clam shells (14, 16) whereby thisswitch (62) has an internal projection (not shown) for engaging with apivotal lever (66) on the switch mechanism (64) so that displacement ofthe switch (62) in a first direction will cause pivotal displacement ofthe pivotal lever (66) in the first direction to connect the batteryterminals to the motor in a first electrical connection and wherebydisplacement of the switch (62) in an opposed direction will effect anopposed displacement of the pivotal lever to reverse the connectionsbetween the battery and the motor. This is conventional to power toolsand will not be described further herein. It will be appreciated that,for clarity, the electrical wire connections between the battery, switchand motor have been omitted to aid clarity in the drawings.

[0047] Furthermore, the power tool (10) is provided with an intelligentlock-off mechanism (68) which is intended to prevent actuation of theactuating trigger (22) when there is no tool head attachment connectedto the body portion (10). Such a lock-off mechanism serves a dualpurpose of preventing the power tool from being switched on accidentallyand thus draining the power source (battery) when not in use whilst italso serves as a safety feature to prevent the power tool being switchedon when there is no tool head attached which would present exposed highspeed rotation of the cog (50).

[0048] The lock-off mechanism (68) comprises a pivoted lever switchmember (70) pivotally mounted about a pin (72) integrally moulded withthe clam shell (16). The switch member (70) is substantially an elongateplastics pin having at its innermost end a downwardly directedprojection (74) (FIG. 5a) which is biassed by conventional spring member(not shown) in a downward direction to the position shown in FIG. 5a soas to abut and engage a projection (76) integral with the actuatingtrigger (22). The projection (76) on the trigger (20) presents arearwardly directed shoulder which engages the pivot pin projection (74)when the lock-off mechanism (68) is in the unactuated position as shownin FIG. 5a.

[0049] In order to operate the actuating trigger (22) it is necessaryfor the user to depress the trigger (20) with their index finger so asto displace the trigger switch (22) from right to left as viewed in FIG.5a. However, the abutment of the trigger projection (76) against theprojection (74) of the lock-off mechanism restrains the trigger switch(20) from displacement in this manner.

[0050] The opposite end of the switch member (70) has an outwardlydirected cam surface (78) being inclined to form a substantiallyinverted V-shaped profile as seen in FIGS. 1 and 6.

[0051] The cam surface (78) is recessed inwardly of an aperture (80)formed in the two halves of the clam shell. As such, the lock-offmechanism (68) is recessed within the body of the tool but is accessiblethrough this aperture (80).

[0052] As will be described later, each of the tool heads (40, 42) to beconnected to the tool body comprise a projection member which, when thetool heads are engaged with the tool body, will project through theaperture (80) so as to engage the cam surface (78) of the lock-offmechanism to pivotally deflect the switch member (70) about the pin (72)against the resilient biassing of the spring member, and thus move theprojection (74) in an upwards direction relative to the unactuatedposition shown in FIG. 5, thus moving the projection (74) out ofengagement with the trigger projection (76) which thus allows theactuating trigger (22) to be displaced as required by the user to switchthe power tool on as required. Thus, attachment of a tool head canautomatically deactivate the lock-off mechanism.

[0053] In addition, an additional feature of the lock-off mechanismresults from the requirement, for safety purposes, that certain toolhead attachments to form particular tools—notably that of areciprocating saw—necessitate a manual, and not automatic, deactivationof the lock-off mechanism. Whereas it is acceptable for a power toolsuch as a drill or a sander to have an actuating trigger switch (22)which may be depressed when the tool head is attached, without anysafety lock-off switch, the same is generally unacceptable for toolssuch as reciprocating saws, whereby accidental activation of areciprocating saw power tool could result in serious injury if the useris not prepared. For this reason, reciprocating saw power tools have amanually operable switch to deactivate any lock-off mechanism on theactuating trigger (22). A specific manually activated mechanism fordeactivating the lock-off mechanism will be described subsequently withreference to the tool head for the reciprocating saw (42).

[0054] Each of the tool heads (40, 42) are designed for co-operatingengagement with the tool body (12). As such, each of the tool heads (40,42) have a common interface (90) for co-operating engagement with thebody (12). The interface (90) on the tool heads comprises a rearwardlyextending surface member (93) which comprises a substantially firstlinear section (91) (when viewed in profile for example in FIG. 8) and asecond non-linear section (95) forming a substantially curved profile.The profile of this surface member (93) corresponds to a similar profilepresented by the external surface of the clam shells of the power tool(12) about the cog member (51) and associated recess (52) as best seenin FIG. 4. The interface (90) further comprises a concentric array oftwo spigots (92, 96) which are so positioned on the substantially flatinterface surface (91) so as to be received in a complementary fitwithin the recess (52) and the associated circular aperture (60) formedin the tool body. The configuration of the interface (90) is consistentwith all tool heads irrespective of the actual function and overalldesign of such tool heads.

[0055] Referring now to FIGS. 1 and 6, it will be appreciated that thefront portion of the tool body (12) for receiving the tool headcomprises both the recess (52) for receiving the spigot (92) of the toolhead and secondly comprises a lower curved surface presenting a curvedseat for receiving a correspondingly curved surface (45) of the toolhead interface (90). This feature will be described in more detailsubsequently.

[0056] The spigot arrangement of the interface (90) has a primary spigot(92) formed substantially as a square member (FIGS. 9 and 10a) havingrounded corners. This spigot (92) corresponds in depth to the depth ofthe recess (52) of the tool body and is to be received in acomplimentary fit therein. Furthermore, the spigot (92) has, on eitherside thereof, two longitudinally extending grooves (100) as best seen inFIGS. 8 and 10a. These grooves taper inwardly from the rearmost surface(93) of the spigot towards the tool head body. Corresponding projections(101) are formed on the inner surface of the skirt (56) of the toolrecess (52) for co-operating engagement with the grooves (100) on thetool head. The projections (101) are also tapered for a complimentaryfit within the grooves (100). These projections (101) and grooves (100)serve to both align the tool head with the tool body and restrain thetool head from rotational displacement relative to the tool body. Thisaspect of restraining the tool head from a rotational displacement isfurther enhanced by the generally square shape of the spigot (92)serving the same function. However, by providing for tapered projections(101) and recesses (100) provides an aid to alignment of the tool headto the tool body whereby the remote narrowed tapered edge of theprojections (101) on the tool body firstly engage the wider profile ofthe tapered recesses (100) on the tool head thus alleviating therequirement of perfect alignment between the tool head and tool bodywhen first connecting the tool head to the tool body. Subsequentdisplacement of the tool head towards the tool body causes the taperedprojections (101) to be received within the tapered grooves (100) toprovide for a close fitting wedge engagement between the projections andthe associated recesses (100). It will be further appreciated from FIG.9 that whilst we have described the spigot (92) as being substantiallysquare, the spigot (92) has an upper edge (111) having a dimensiongreater than the dimension of the lower edge (113). This is a simpledesign to prevent accidentally placing the head attachment “upside down”when bringing it into engagement with the tool body, since if the toolhead spigot (92) is not correctly aligned with the recess (52) it willnot fit.

[0057] As seen in FIG. 8 and FIG. 10a, the common interface (90) has asecond spigot member (96) in the form of a substantially cylindricalprojection extending rearwardly of the first spigot member (92). Thesecond spigot member (96) may be considered as coaxial with the firstspigot member (92). The second spigot member (96) is substantiallycylindrical having a circular aperture (102) extending through thespigot (92) into the interior of the tool head. Mounted within both thedrill tool head (40) and jigsaw tool head (42), adjacent theirrespective apertures (102), is a further standard sun and planet gearreduction mechanism (106) (FIGS. 10b and 13). It should be appreciatedthat the arrangement of the interface member (90) is substantiallyidentical between the two heads (40, 42) and the placement of the gearreduction mechanism (106) within each tool head with respect to theinterface (90) is also identical for both tool heads and thus, bydescription of the gear mechanism and interface members (90) of the toolhead in respect of the jigsaw head (42), a similar arrangement isemployed within the drill tool head (40) (FIG. 13).

[0058] As seen in FIG. 10b, the tool heads are again conventionallyformed from two halves of a plastic clam shell. The two halves arefitted together to encapsulate the internal mechanism of the power toolhead to be described as follows. Internally moulded ribs on each of thetwo halves of the clam shell forming each tool head are used to supportthe internal mechanism and, in particular, the jigsaw tool head (42) hasribs (108) for engaging and mounting the gear reduction mechanism (106)as shown. The gear reduction mechanism (106), as mentioned above, is aconventional epicyclic (sun and planetary arrangement) gearbox identicalto that as described in relation to the epicyclic gear arrangementutilised in the tool body. The input spindle (not shown) of the gearreduction mechanism (106) has coaxially mounted thereon a female cog(110) for co-operating meshed engagement with the male cog (50) of thepower tool body. The spindle of the gear mechanism (106) and the femalecog (110) extend substantially coaxial with the aperture (102) of thespigot (96) about the tool head axis (117). This is best seen in FIG.10a. Furthermore, the rotational output spindle (127) of this gearmechanism (106) also extends coaxial with the input spindle of the gearmechanism.

[0059] Again referring to FIG. 10b, it will be seen that the rotationaloutput spindle (127) has mounted thereon a conventional motionconversion mechanism (120) for converting the rotary output motion ofthe gear mechanism (106) to a linear reciprocating motion of a platemember (122). A free end of the plate member (130) extends outwardly ofan aperture in the clam shell and has mounted at this free end a jigsawblade clamping mechanism. This jigsaw blade clamping mechanism does notform part of the present invention and may be considered to be any oneof a standard method of engaging and retaining jigsaw blades on a platemember.

[0060] The linear reciprocating motion of the plate member (122) drivesa saw blade (not shown) in a linear reciprocating motion indicatedgenerally by the arrow (123). Whilst it can be seen from FIG. 10b thatthis reciprocating motion is not parallel with the axis (117) of thetool head, this is merely a preference for the ergonomic design of theparticular tool head. If necessary, the reciprocating motion could bemade parallel with the tool head axis. The tool head (42) itself is aconventional design for a reciprocating or pad saw having a base plate(127) which is brought into contact with the surface to be cut in orderto stabilise the tool (if required).

[0061] The drive conversion mechanism (120) utilises a conventionalreciprocating space crank illustrated, for clarity, schematically inFIG. 10c. The drive conversion mechanism (120) will have a rotary input(131) (which for this particular tool head will be the gear reductionmechanism). The rotary input (121) is connected to a link plate (130)having an inclined front face (132) (inclined relative to the axis ofrotation of the input). Mounted to project proud of this surface (132)is a tubular pin (134) which is caused to wobble in reference to theaxis (117) of rotation of the input (130). Freely mounted on this pin(134) is a link member (135) which is free to rotate about the pin(134). However this link member (135) is restrained from rotation aboutthe drive axis (117) by engagement with a slot within a plate member(122). This plate member (122) is free (in the embodiment of FIGS. 10band 10 c) to move only in a direction parallel with the axis of rotationof the input. The plate member (127) is restrained by two pins (142)held in place by the clam shell and is enabled to pass therethrough.Thus, the wobble of the pin (134) is translated to linear reciprocatingmotion of the plate (122) via the link member (135). This particularmechanism for converting rotary to linear motion is conventional and hasonly been shown schematically for clarification of the mechanism (120)employed in this particular saw head attachment. In the saw head (42)the plate (122) is provided for reciprocating linear motion between thetwo restraining members (142) and has attached at a free end thereof ablade clamping mechanism (150) for engaging a conventional saw blade ina standard manner. Thus the tool head employs both a gear reductionmechanism (106) and a drive conversion mechanism (120) for convertingthe rotary output of the motor to a linear reciprocating motion of theblade.

[0062] An alternative form of tool head is shown in FIG. 13 with respectto a drill head (40). Again this drill head (40) (also shown in FIG. 8a)comprises the interface (90) corresponding to that previously describedin relation to tool head (42). The tool head (40) again comprises aepicyclic gearbox (106) similar in construction to that previouslydescribed for both the power tool and the jigsaw head. The input spindleof this gear reduction mechanism (106) again has co-axially mountedthereon a female cog similar to that described with reference to the sawhead for meshed engagement with the male cog (50) on the output spindleof the power tool. The output of the epicyclic gearbox (106) in the toolhead (40) is then co-axially connected to a drive shaft of aconventional drill clutch mechanism (157) which in turn is co-axiallymounted to a conventional drill chuck (159).

[0063] It will be appreciated that for the current invention of a powertool having a plurality of interchangeable tool heads, that the outputspeed of various power tools varies from function to function. Forexample, a sander head (although not described herein) would require anorbital rotation output of approximately 20,000 rpm. A drill may requirea rotational output of approximately 2-3,000 rpm, whilst a jigsaw mayhave a reciprocal movement of approximately 1-2,000 strokes per minute.The conventional output speed of a motor as used in power tools may bein the region of 20-30,000 rpm thus, in order to cater for such a vastrange of output speeds for each tool head, derived from a single highspeed motor, would require various sized gear reduction mechanisms ineach head. In particular for the saw head attachment, significantreduction of the output speed would be required and this would probablyrequire a large multi-stage gearbox in the jigsaw head. This would bedetrimental to the performance of a drill of this type since such alarge gear reduction mechanism (probably multi-stage gearbox) wouldrequire a relatively large tool head resulting in the jigsaw blade beingheld remote from the power saw (motor) which could result in detrimentalout of balance forces on such a jigsaw. To alleviate this problem, thecurrent invention employs the use of sequentially or serially coupledgear mechanisms between the tool body and the tool heads. In thismanner, a first stage gear reduction of the motor output speed isachieved for all power tool functions within the tool body whereby eachspecific tool head will have a secondary gear reduction mechanism toadjust the output speed of the power tool to the speed required for theparticular tool head function. As previously mentioned, the exact ratioof gear reduction is dependent upon the size and parameters of theinternal mechanisms of the standard epicyclic gearbox but it will beappreciated that the provision for a first stage gear reduction in thetool head to then be sequentially coupled with a second stage gearreduction in the tool body allows for a more compact design of the toolheads whilst allowing for a simplified gear reduction mechanism withinthe tool head since such a high degree of gear reduction is not requiredfrom the first stage gear reduction.

[0064] In addition, the output of the second stage gear reduction in thetool head may then be retained as a rotational output transmitted to thefunctional output of the tool head (i.e. a drill or rotational sandingplate) or may itself undergo a further drive conversion mechanism toconvert the rotary output into a non-rotary output as described for thetool head in converting the rotary output to a reciprocating motion fordriving the saw blade.

[0065] The saw tool head (42) is also provided with an additionalmanually operable button (170) which, on operation by the user, providesa manual means of deactivating the lock-off mechanism of the power toolbody when the tool head (42) is connected to the tool body. Aspreviously described, the tool body has a lock-off mechanism (68) whichis pivotally deactivated by insertion of an appropriate projection onthe tool head into the aperture (80) to engage the cam surface (78) todeactivate the pivoted lock-off mechanism. Usually the projection on thetool head is integrally moulded with the head clam shell so that as thetool head is introduced into engagement with the tool body suchdeactivation of the lock-off mechanism is automatic. In particular, withreference to FIGS. 9 and 13 showing the drill tool head (40), it will beseen that the interface (90) has on the curved surface (93) asubstantially rectangular projection (137) of complimentary shape andsize to the aperture (80). This projection (137) is substantially solidand integrally moulded with the clam shell of the tool head. In use asit enters through the aperture (80) this solid projection (137) simplyabuts the cam surface (78) to effect pivotal displacement of thelock-off mechanism (68). However, for the purposes of products such asreciprocating saw heads (42) it is further desirable that activation ofthe power tool, even with the tool head attached, is restricted until afurther manual operation is performed by the user when they are ready toactually utilise the tool. Thus, the saw head (42) is provided with thebutton (170) to meet this requirement. This manual lock-off deactivationsystem comprises a substantially rectangular aperture (141) formedbetween two halves of the tool head clam shell as shown in FIG. 10athrough which projects a cam member (300) which is substantiallyV-shaped (FIGS. 10a and 10 c). This cam member (300) has a generalV-shaped configuration and orientation so that when the saw head (42) isattached to the tool body (12), the cam surface (78) of the lock-offmechanism is received within the inclined V-formation of this cam member(300) without any force being exerted on the cam member (78) todeactivate the lock-off mechanism.

[0066] Referring now to FIGS. 10c and 10 d, it can be seen that the cammember (300) is connected by a leg (301) to the mid region of a plasticsmoulded longitudinally extending bar (302) to form an actuation member(350). This bar (302), when mounted in the tool head (42) extendssubstantially perpendicular to the axis of the tool head (and to theaxis (117) of the tool body) so that each of the free ends (306) of thebar (302) projects sideways from the opposed side faces of the tool head(FIG. 10a) to present two external buttons (only one of which is shownin FIG. 10a). Furthermore, the bar member (302) comprises two integrallyformed resiliently deflectable spring members (310) which, when the barmember (302) is inserted into the tool head clam shells, each engageadjacent side walls of the inner surface of the clam shell, serving tohold the bar member substantially centrally within the clam shell tomaintain the cam surface (300) at a substantially central orientation asit projects externally at the rear of the tool head through the aperture(141). A force exerted to either face (306) of the bar member (302)projected externally of the tool head will displace the bar memberinwardly of the tool head against the resilience of one of the springmembers (310), whereby such displacement of the bar member effectscomparable displacement of the cam member (300) laterally across theaperture (141). It will therefore be appreciated that, dependent onwhich of the two surfaces (306) are depressed, the cam member (300) maybe displaced in either direction transversely of the tool head axis. Inaddition, when the external force is removed from the surface (306), thebiassing force of the spring member (310) (which is resilientlydeformed) will cause the bar member (302) to return to its originalcentral position. For convenience, this cam and bar member (300 and 302)comprise a one-piece moulded plastics unit with two spring members (310)moulded therewith.

[0067] When the tool head (42) is attached to the tool body (12) (aswill be described in greater detail later) the cam surface (78) of thelock-off mechanism is received in co-operating engagement within theV-shaped configuration of the cam surface (300). The cam surface (78)(as seen in FIGS. 1 and 6) has a substantially convex configurationextending along its longitudinal axis and having two symmetrical camfaces disposed either side of a vertical plane extending along thecentral axis of the member (70). Whereas the cam surface (300) has acorresponding concave cam configuration having two symmetrical cam facesinversely orientated to those cam faces of cam (78) to provide for abutting engagement between the two cam surfaces. When the tool head (42)is attached to the tool body, the concave cam surfaces (300)co-operatingly receives the convex cam surfaces (78) in a close fit sothat no undue force is exerted from the cam surface (300) to the camsurface (78) so as to deactivate the lock-off mechanism which remainsengaged with the switch (22) preventing operation of the power tool.This prevents the power saw configuration from being accidentallyswitched on. When the tool is desired to be operated, the user willplace one hand on the pistol grip (18) so as to have the index fingerengaged to the switch (22). A second hand will then grip the tool headattachment (42) in a conventional manner for operating a reciprocatingsaw, the second hand serving to stabilise the saw in use. The userssecond hand will then serve to be holding the power tool adjacent one ofthe projecting surfaces (306) or the actuating member (350) which isreadily accessible by finger or thumb of that hand. When the operatorwishes to then start using the tool he may depress one of the surfaces(306) with his thumb or forefinger to cause lateral displacement of thecam surface (300) with regard to the tool head axis, causing an inclinedsurface (320) of the convex surface (300) to move sideways intoengagement with one of the convex inclined surfaces of the cam surface(78), effectively displacing the cam surface (78) downwardly withrespect to the tool body, thereby operating the lock-off mechanism (68)in a manner similar to that previously discussed with regard to theautomatic lock-off deactivation mechanism.

[0068] When the surface (306) is released by the operator the camsurface (300) returns to its central position under the resilientbiassing of the spring members (310) and out of engagement with the camsurface (78). However, due to the trigger switch remaining in theactuated position, the lock-off member (68) is unable to re-engage withthe switch until that switch (22) is released. Thus when one of theactuating member buttons (306) on the tool head is depressed, the powertool may be freely used until the switch (22) is subsequently released,at which time if the user wishes to recommence operation he will againhave to manually deactivate the lock-off mechanism by depressing one ofthe buttons (306).

[0069] Referring now to FIGS. 11 and 12 (showing a cross-section of thegear reduction mechanism of the tool body), it will be appreciated thatthe output spindle of the gear reduction mechanism and the male cogmember (50) mounted thereon are substantially surrounded by a circularcollar (400) coaxial with the axis of the output spindle. As best seenin FIG. 5b it will be appreciated that the male cog (50) and thisconcentric collar (400) project through the circular aperture (60) inthe tool surface (54) into the recess (52) of the power tool. Theexternal diameter of the collar (400) on the gear reduction mechanism(48) corresponds to the internal diameter of the aperture (102) of thespigot (96) on each of the tool heads. The collar (400) also has twoaxially extending diametrically opposed rebates (410) which taperinwardly towards the gear reduction mechanism (48). Furthermore,integrally formed on the internal surface of the aperture (102) of thespigot member (96) are two corresponding projections (105),diametrically opposed about the tool head axis (117) and here taperoutwardly in a longitudinal direction towards the gear reductionmechanism of the tool head.

[0070] When the tool head is brought into engagement with the tool bodythe collar (400) of the reduction mechanism in the tool body is receivedin a complementary fit within the aperture (102) of the tool head withthe projections (105) on the internal surface of the aperture (102)being received in a further complementary fit within the rebates (410)formed in the outer surface of the collar member (400). Again, due tothe complimentary tapered effect between the projections (105) and therebates (410) a certain degree of tolerance is provided when the toolhead is first introduced to the tool body to allow alignment between thevarious projections and rebates with continued insertion graduallybringing the tapered surfaces of the projections and rebates intocomplimentary wedged engagement to ensure a snug fit between the toolhead and the tool body and the various locking members.

[0071] This particular arrangement of utilising first (92) and second(96) spigots on the tool head for complementary engagement with recesseswithin the tool body provides for engagement between the tool head andthe clam shell of the tool body and further provides for engagementbetween the clam shell of the tool head and of the gear reductionmechanism, and hence rotary output, of the tool body. In this manner,rigid engagement and alignment of the output spindle of the gearmechanism of the tool body and the input spindle of the gear reductionmechanism of the tool head is achieved whilst also obtaining a rigidengagement between the clam shells of the tool head and tool body toform a unitary power tool by virtue of the integral engagement of therespective gear mechanisms.

[0072] Where automatic deactivation of the lock-off mechanism (68) isrequired, such as when attaching a drill head to the tool body, asubstantially solid projection (137) is formed integral with the clamshell surface (FIGS. 9 and 13) which presents a substantiallyrectangular profile which, as the tool head (40) is engaged with thetool body (12) the projection (137) co-operates with the rectangularaperture communicating with the pivotal lever (66) so as to engage thecam surface (78) and effect pivotal displacement of the pivoted lever(66) about the pin member (72) so as to move the downwardly directedprojection (74) out of engagement with the projection (76) on theactuating trigger (20). Thus, once the drill head (40) has been fullyconnected to the body (12) the lock-off mechanism is automaticallydeactivated allowing the user freedom to use the power tool viasqueezing the actuating trigger (22).

[0073] It will also be appreciated from FIGS. 8 through 10 that theinterface (90) of each of the tool heads (40, 42) comprise twoadditional key-in members formed integrally on the clam shell of thetool head. The spigot (92) has on its outermost face (170) asubstantially inverted “T” shaped projection extending parallel with theaxis (117) of the tool head axis. This projection is received within aco-operating aperture on the inner surface (54) of the recess (52) ofthe tool body. A further, substantially rectangular, projection (172) isdisposed on the interface (90) below the automatic lock-off projection(137) when viewed in FIGS. 8 and 9 again for co-operating engagementwith a correspondingly shaped recess (415) formed in the surface of theclam shell of the tool body. These key-in projections again serve tohelp locate and restrain the tool head in its desired orientation on thetool body.

[0074] To restrain the tool head (40, 42) from axial displacement fromthe tool body once the tool head and tool body have been brought intoengagement (and the various projections and rebates between the toolhead and tool body have been moved into co-operating engagement), areleasable detent means, which in the specific embodiment is a springmember, is mounted on the tool body so as to engage with the interface(90) of the tool head to restrain the tool head from relativedisplacement axially out of the tool body. The engagement between thedetent means (spring) and the interface (90) of the tool head providesfor an efficient interlock mechanism between the tool head and the toolbody.

[0075] The spring member (200) comprises two resiliently deflectablearms (201) which, in this preferred embodiment, are comprised in asingle piece spring as shown in FIG. 7c. The spring member (202) isrestrained in its desired orientation within the clam shell of the toolbody by moulded internal ribs (207) on the tool clam shell (FIG. 5b).Spring member (202) is substantially U-shaped wherein the upper ends(209) of both arms of this U-shaped spring taper inwardly by means of astep (211) to form a symmetrical U-shaped configuration having a narrowneck portion. The free ends (213) of the two arms are then foldedoutwardly at 90° to the arm members as best shown in FIG. 7c.

[0076] The spring mechanism (200) further comprises a release button(208) (which serves as an actuator means for the spring) as best seen inFIG. 7a. This button (208) comprises two symmetrically opposed rebates(210) each having inner surfaces for engaging the spring member (202) inthe form of inner cammed faces (212) as best seen in FIG. 7b whichrepresents a cross-section of the button members (208) along the linesVII-VII (through the rebates (210)) in FIG. 7a. It will be appreciatedthat these inner cammed faces (212) comprise two cammed surfaces (214and 216), forming a dual gradient surface, which are inclined atdifferent angles to the vertical. The first cam surface (214) is setsubstantially 63° to the vertical and the second cam surface (216) isset at substantially 26° to the vertical. However it will be appreciatedthat the exact degree of angular difference to the vertical is not anessential element of the present invention save that there is asignificant difference between the two relative angles of both camsurfaces. In particular, the angle range of the first cam surface (214)may be between 50° and 70° whereas the angle of the second cam surface(216) may be between 15 and 40°.

[0077] In practice, the two free ends of the spring member (202) are oneeach received in the two opposed rebates (210) of the release button(208). In the tool body clam shells, the button (208) is restrained bymoulded ribs (219) on each of the clam shells from lateral displacementrelative to the tool axis. However, the button itself is received withina vertical recess within the clam shell allowing the button to bemoveable vertically when viewed in FIG. 5 into and out of the clamshell. The clam shell further comprises a lower rib member (227) againstwhich the base (203) of the U-shaped spring member (202) abuts.Engagement of the free ends of the spring member (202) with the camsurfaces of the rebates (210) of the release button (208) serve toresiliently bias the button in an unactuated position whereby the uppersurface of the button (208) projects slightly through an aperture in theclam shell of corresponding dimension. The button (208) furtherincorporates a shoulder member (211) extending about the periphery ofthe button which engages with an inner lip (not shown) of the body clamshell to restrain the button from being displaced vertically out of theclam shell.

[0078] In operation, depression of the button member (208) effects camengagement between the upper shoulder members (230) of the U-shapedspring with the inner cam faces (212) of the button rebates (210).Spring member (202) is prevented from being displaced verticallydownwards by depression of the button by the internal rib member (217)upon which it sits. Furthermore, since the button member (208) isrestrained from any lateral displacement relative to the clam shell bymeans of internal ribs, then any depressive force applied to the buttonis symmetrically transmitted to each of the arm members by thesymmetrically placed rebates (210). As the first cam surface (216)engages with the shoulder of the U-shaped spring members the angle ofincidence between the spring member and the cam surface is relativelylow (27°) requiring a relatively high initial force to be transmittedthrough this cam engagement to effect cam displacement of the springmember (against the spring bias) along the cam surface (216) as thebutton is depressed. This cam engagement between the spring member (202)and the first cam (216) surface effectively displaces the two arms ofthe spring member away from each other. Continued depression of thebutton (208) will eventually cause the shoulders (230) of the arms ofthe spring member to move into engagement with the second cam surface(214) whereby the angle of incidence with this steeper cam surface issignificantly increased (64°) whereby less force is subsequentlyrequired to continue cam displacement of the spring member along thesecond cam surface (216).

[0079] Wherein the first cam surface (216) provides for low mechanicaladvantage, but in return provides for relatively high dispersion of thearms of the spring member for very little displacement of the button,when the spring arms engage with the second cam surfaces (216) a highmechanical advantage is enjoyed due to the high angle of incidence ofthe cam surface with the spring member. In use, the user will beapplying a significantly high force to the button when engaging with thefirst cam surface but, when the second cam surface is engaged the enduser continues to apply a high depressive force to the button resultingin rapid displacement of the spring member along the second cam surface(216). The result of which is that continued downward displacement ofthe button is very rapid until a downwardly extending shoulder (217) ofthe button abuts with a restrictive clam shell rib (221) to define themaximum downward displacement of the button. Effectively, the use ofthese two cam surfaces in the orientation described above provides botha tactile and audible feedback to the user to indicate when fulldisplacement of the button has been achieved. By continuing the largedepressive force on the button when the second cam surface is engagedresults in extremely rapid downward depression of the button as thespring relatively easily follows the second cam surface resulting in asignificant increase in the speed of depression of the button until itabuts the downward limiting rib of the clam shell. This engagement ofthe button with the clam shell rib (221) provides an audible “click”clearly indicating to the end user that full depression has beenachieved. In addition, as the button appears to snap downward as thespring member transgresses from the first to second cam surfaces thisprovides a second, tactile, indication to the user that full depressionhas been achieved. Thus, the spring mechanism (200) provides a basicallydigital two-step depression function to provide feedback to the userthat full depression and thus spreading of the retaining spring (202)has been achieved. As such, an end user will not be confused intobelieving that full depression has been achieved and thereby try toremove a tool head before the spring member has been spreadsufficiently.

[0080] The particular design of the spring mechanism (200) has twoadditional benefits. Firstly, the dual gradient of the two cam surfaces(214 and 216) provides additional mechanical advantage as the button isdepressed, whereby as the arms of the spring member are displaced apartthe resistance to further displacement will increase. Therefore the useof a second gradient increases the mechanical advantage of the camdisplacement to compensate for this increase in spring force.

[0081] Furthermore, it will be appreciated that the dimensions of thespring to operate in retaining a tool head within the body are requiredto be very accurate which is difficult to achieve in the manufacture ofsprings of this type. It is desired that the two arms of the springmember in the unactuated position are held a predetermined distanceapart to allow passage of the tool head into the body of the toolwhereby cam members on the tool head will then engage and splay the armsof the spring members apart automatically as the head is introduced, andfor those spring members to spring back and engage with shoulders on thespigots to effect snap engagement. This operation will be described inmore detail subsequently.

[0082] However, if the arms of the spring member are too far apart thenthey may not return to a closed neutral position sufficient to effectretention of the tool head. If the arms are too close together then theymay not receive the cam members on the tool head or make it difficult toreceive such cam members to automatically splay the spring member.Therefore, in order that the tolerance of the spring member may berelaxed during manufacture, two additional flat surfaces (230) of thebutton (FIG. 7b) are utilised to engage the inner faces of the two arms(at 290) of the spring member to retain those arms at a correctlypredetermined distance so as to effect maximum mechanical engagementwith the spigot of the tool head.

[0083] To co-operate with the spring member (200), the second spigot(96) of the interface (90) further comprises two diametrically opposedrebates (239) in its outer radial surface for co-operating engagementwith the arms (201) of the spring member (202) when the tool head isfully inserted into the tool body.

[0084] Referring now to FIGS. 8, 8a, 9 and 10 a, the substantiallycylindrical secondary spigot (96) of each interface (90) of the varioustool heads comprises two diametrically opposed rebates or recesses (239)radially formed within the wall of the spigot (96). The inner surface oftheses rebates (239) whilst remaining curved, are significantly flatterthan the circular outer wall (241) as best seen in FIG. 8a showing across-section through lines 8-8 of FIG. 8. These surfaces (240) have avery large effective radius, significantly greater than the radius ofthe spigot (96). In addition, the rebates (239) have, when viewed inFIGS. 8 and 8a, a shoulder formed by a flat surface (247) which flatsextend substantially parallel with the axis of the spigot (92).

[0085] It will be appreciated that when the two arms (201) of the springmember (202) are held, in their rest position (defined by the widthbetween the two inner flats (230) of the button member and showngenerally in FIG. 7c as the distance A), they are held at a distancesubstantially equal to the distance B shown in FIG. 8a between theopposed inner surfaces of the two rebates (239). In practice, once thetool head has been inserted into the tool body the rebates (239) are inalignment between the two arms of the spring member (202) so that thesearms engage the rebate under the natural bias of such spring. In thisposition the shoulders (211) formed in the spring member engage with thecorresponding shoulders (243) formed in the rebate (239). Due to thesignificant flattening effect of the otherwise circular spigot createdby these rebates, a greater surface area of the spring member (202) willengage and abut within the rebate (239) than if simply two parallelwires were to engage with a circular rebate. Significantly more contactis effected between the spring member and the rebate by this currentdesign.

[0086] In addition, the rebates (239) each have associated lead-in camsurfaces (250) disposed towards the outer periphery of the cylindricalspigot (96), which cam surfaces (250) extend substantially along atangent of the spigot (96) wall and substantially project beyond thecircumference of the spigot (96) as seen in FIGS. 8b, 9 and 10 a. Thesecam surfaces (25) extend both in a direction parallel to the axis of thecylindrical spigot (96) and in a direction radially outward of thespigot wall. These cam surfaces comprise a chamfer which extends in anaxial direction away from the free end of the spigot (96) radiallyoutwardly of the axis (117) of the tool head. Finally, when viewingthese cam surfaces (250) with reference to FIG. 9, it will be seen thatthe cam surfaces partially extends about the side wall and generallyhave a profile corresponding to the stepped shape of the arms of theU-shaped spring member (202). The general outer profile of the camsurfaces (250) correspond to a similar shape formed by the innersurfaces (240) of the rebates (239) and serves to overlie these rebates.In particular, the cam surfaces (250) have a substantially flat portionwhen viewed in FIG. 9 (257) and a substantially flattened curved portion(258) leading into a substantial flat cam surface (261) overlying thecorresponding flat surface (247) of the associated rebate (239). Againit will be appreciated that the profile of these cam surfaces, whenpresented to the tool head correspond substantially to the profilepresented by the spring member (202) with the curved portion of the camsurface (258) corresponding substantially to the shoulders (211) formedin the spring member (202) and the substantially flat cam surfaces(261), disposed symmetrically about the spigot (96), corresponding indiameter to the distance between the inner neck portions (209) andspring members (202).

[0087] In practice as the tool head (40/42) is inserted into the toolbody, the cam surface (250) will engage with the arms (201) of thespring member to effect resilient displacement of these spring membersunder the force applied by the user in pushing the head and bodytogether to effect cam displacement of the spring members over the camsurface (250) until the spring members engage the rebates (239), wherebythey then snap engage, under the resilient biassing of the springmember, into these rebates. Since the inner surfaces of the cam surfaces(250) are substantially flat the spring member then serves to retain thetool head from axial displacement away from the body (12).

[0088] It will be appreciated that the circular aperture (60) formed inthe inner surface (54) of the recess (52) of the tool body, whilstsubstantially circular does, in fact, comprises a profile correspondingto the cross-sectional profile presented by the spigot (96) andassociated cam surfaces (250). This is to allow passage of the spigotthrough this aperture (60). As seen in FIG. 6, the arms of the springmember (202) (shown shaded for clarity) project inwardly of thisaperture (60) so as to effect engagement with the rebates (240) on thespigot (96) of a tool head mounted on the tool body when the springmember is in an unactuated position.

[0089] Also seen in FIG. 10a, the outer radial surface of the spigot(96) and the associated cam surfaces (250) have a second channel (290)extending parallel with the axis (117) of the tool head. Each of thesediametrically opposed rebates correspond with two moulded ribs formed onthe clam shell so as to project radially into the aperture (60) in thetool body, one each disposed on either side of the body axis wherebysuch ribs are received within a complimentary fit within the tool headchannel (290) when the spigot (96) is inserted into the tool body. Theseadditional ribs and channels (290) serve to further effect engagementbetween the tool body and the tool head to retain the tool head from anyform of relative rotational displacement when engaged in the tool body.

[0090] It will now be appreciated from the foregoing description thatconsiderable mechanisms for aligning and connecting and restraining thetool head to the tool body are employed in the present invention. Inparticular, this provides for an accurate method of coupling together apower tool body with a power tool head to form a substantially rigid andwell aligned power tool. Since power tools of this type utilise a drivemechanism having a first axis in the power tool to be aligned with anoutput drive mechanism on the tool head having a second axis, it isimportant that alignment of the tool head to the tool body is accurateto ensure alignment of the two axes of the tool head and tool body toobtain maximum efficiency. The particular construction of the power tooland tool heads of the present invention have been developed to providean efficient method of coupling together two component parts of a powertool to obtain a unitary tool. The tool design also provides for apartially self-aligning mechanism to ensure accurate alignment betweenthe tool head and tool body. In use, a user will firstly generally aligna tool head with a tool body so that the interface (90) of the tool headand the respective profile of the flat and curved surfaces of the toolhead align with the corresponding flattened curved surfaces of the toolbody in the region of the recess (52). The first spigot member (92) isthen generally introduced to the correspondingly shaped recess (52)wherein the substantially square shape of the spigot (92) aligns withthe co-operating shape of the recess (52). In this manner, the widerremote ends of the channels (101) in the spigot (92) are substantiallyaligned with the narrower outwardly directed ends of the co-operatingprojections (101) mounted inwardly of the skirt (56) of the recess (52).Respective displacement of the head towards the body will then cause thetapered channels (100) to move into wedge engagement with thecorrespondingly tapered projections (101) to help align the tool headmore accurately with the tool body which serves to subsequently alignthe second cylindrical spigot with the collar (400) of the gearreduction mechanism in the tool body which is to be received within thespigot (96). Furthermore, the internal tapered projections (105) of thespigot (96) are aligned for co-operating engagement with thecorrespondingly tapered rebates (410) formed on the outer surface of thecollar member (400). Here it will be appreciated that the spigot (96) isreceived within the aperture (60) of the surface member (54) of therecess (52). In this manner, it will be appreciated that the clam shellof the tool head is coupled both directly to the clam shell of the toolbody and also directly to the output drive of the tool body. Finally,continued displacement of the tool head towards the tool body will thencause the cam surfaces (250) of the spigot (96) to abut and engage withthe spring member (202) whilst the teeth of the male cog (50) arereceived within co-operating recesses within the female cog member ofthe tool head, the cam surfaces on the male cog (50) serving to alignthese teeth with the female cog member.

[0091] As the tool head is then finally pushed into final engagementwith the tool body, the chamfered cam surfaces (250) serve to deflectthe arms of the spring member (202) radially outwards as the spigot (96)passes between the arms of the spring member until the arms of thespring member subsequently engage the channel (239) whereby they thensnap engage behind the cam surfaces (250) to lock the tool head fromaxial displacement out of engagement with the tool body.

[0092] As previously discussed, to then remove the tool head from thetool body the button (208) must be displaced downwardly to splay the twoarms of the spring member (202) axially apart out of the channel (239)to allow the shoulders presented by the cam surfaces (205) to then passbetween the splayed spring member (202) as it is moved axially out ofengagement with the drive spindle of the tool body.

[0093] When the tool heads (40 and 42) have been coupled with the mainbody (12) in the manner previously described, then the resultant powertool (10) will be either a drill or a circular saw dependent on the toolhead. The tool is formed having a double gear reduction by way of thesequential engagement between the gear reduction mechanisms in the toolhead and tool body. Furthermore, as a result of the significantengagement and alignment between the tool head and tool body by virtueof the many alignment ribs and recesses between the body and tool heads,the drive mechanisms of the motor and gear reduction mechanisms may beconsidered to form an integral unit as is conventional for power tools.

[0094] As seen from FIG. 10a and FIGS. 2 and 3, the interface (90)further comprises a substantially first linear section (91) (when viewedin profile) from which the spigot members (92 and 96) extend and asecond non-linear section forming a curved profile. This profile may bebest viewed in FIG. 8. The profile of the power tool body (12) at thearea of intersection with the tool head corresponds and reciprocatesthis profile for complimentary engagement as in FIGS. 2, 3 and 4. Whilstthis profile may be aesthetically pleasing, it further serves afunctional purpose in providing additional support about this interfacebetween the tool heads and tool body. To those skilled in the art, itwill be appreciated that the use of a power drill requires applicationof a force substantially along the drive axis of the motor and drillchuck. For the current embodiment whereby there is an interface betweenthe tool body and tool head then transmission of this force will bedirectly across the substantially linear interface region (91). Inaddition, any toroidal forces exerted by the rotational motion of thedrill chuck and motor across the interface are firstly resisted by thesubstantially square spigot member (92) being received in asubstantially square recess (52) and is further resisted by engagementbetween the ribs (101) on the recess (52) engaging with correspondingrebates (100) formed on the spigot (92). However, it is to be furtherappreciated that engagement of the curved section (95) of the interface(90) will also resist rotational displacement of the tool head relativeto the tool body.

[0095] However, with regard to the power tool of a jigsaw, as shown inFIG. 3, the curved interface serves a further purpose of alleviatingundue operational stresses between the tool body and tool head when usedin this saw mode. When viewed in FIG. 3 the operation of the power toolas a jigsaw will result in a torque being applied to the tool head (42)as the saw is effectively pushed along the material being cut (directionD) and the resultant reaction between the saw blade and the woodattempting to displace the tool head in a direction shown generally as“E” in FIG. 3 as opposed to the force being applied to the power tool inthe direction “F” as shown in FIG. 3. If a simple flat interface betweenthe tool head and tool body were here employed then the resultant torquewould create stresses effectively trying to pivot the tool head awayfrom the tool body in the region (500) and effectively creating unduestress on the drive spindles of the various gear reduction mechanismsbetween the tool head and body across the interface. However, by use ofthe curved interface as shown in FIG. 3, a direct force from the powertool body to the power tool head to effect displacement of the powertool in the direction of cutting (D) is transmitted through this curvedinterface rather than relying on the engagement between the spindles ofthe gear mechanisms across the flat interface. Thus the curved interfacehelps to significantly reduce undue torque across the spindle axis ofthe power tool and tool head.

[0096] Additionally, the use of the additional projection member (172)on the tool head (42) (as seen in FIG. 10a) presents at least one flatsurface substantially at right angles to the axis of rotation of themotor and drive spindle to effect transmission of a pushing forcebetween the tool body and tool head substantially at right angles to therelative axis of the tool head and tool body. However, it will beappreciated that the degree of curvature on the curved surface of theinterface may be sufficient to achieve this without the requirement ofan additional projection (172).

[0097] It will be appreciated that the above description relates to apreferred embodiment of the invention only whereby many modificationsand improvements to these basic concepts are conceivable to a personskilled in the art whilst still falling within the scope of the presentinvention.

[0098] In particular, it will be appreciated that the engagementmechanisms between the tool head and the tool body can be reversed suchthat the tool body may comprise the interface (90) with associatedspigots (92 and 96) for engagement with a co-operating front aperturewithin each of the tool heads. In addition, the spring mechanism (200)may also be contained in the tool head in such a situation forco-operating engagement with the spigots thereby mounted on the toolbody.

[0099] Still further, whilst the present invention has been describedwith reference to two particular types of tool head, namely a drill headand a saw head, it will be appreciated that other power tool heads couldbe equally employed utilising this conventional power tool technology.In particular, a head could be employed for achieving a sanding functionwhereby the head would contain a gear reduction mechanism as requiredwith the rotary output of the gear reduction mechanism in the power toolhead then driving a conventional sander using an eccentric drive as iscommon and well understood to those skilled in art. In addition, ascrewdriving function may be desired whereby two or more subsequent gearreduction mechanisms are utilised in sequence within the tool head tosignificantly reduce the rotary output speed of the tool body. Againsuch a feature of additional gear reduction mechanisms is conventionalwithin the field of power tools and will not be described further in anydetail.

1. Interlock mechanism for releasably coupling first and second portionsof a power tool comprising: a spring normally biassed to a first, closedposition; and an actuator co-operable with the spring to urge thespring, under influence of the actuator, into a second, open position,the interlock mechanism characterised by the actuator having aspring-engaging surface formed from a plurality of individual surfaceswhich are not coplanar.
 2. An interlock mechanism according to claim 1,wherein the spring-engaging surface defines a dual-gradient surface. 3.An interlock mechanism according to claim 1, wherein the spring isformed as a U-shaped member, the open arms of which are co-operable withthe actuator.
 4. An interlock mechanism according to claim 3, whereinthe open arms of the spring contact the spring-engaging surface of theactuator such that movement of the actuator causes concomitant movementof the arms of the spring.
 5. An interlock mechanism according to claim4, wherein the open arms of the U-shaped member are not straight.
 6. Aninterlock mechanism according to claim 3, wherein the actuator defines aseat within which at least a portion of the spring sits, the seatincluding a plurality of parallel members arranged to engage with theleast two portions of the spring, thereby to retain the spring in theseat in the first, closed position.
 7. An interlock mechanism accordingto claim 6, wherein the plurality of parallel members comprise twoprojections, each of which projections engages with a corresponding oneof the open arms of the U-shaped member.
 8. An interlock mechanismaccording to claim 3, wherein the actuator has a plurality ofspring-engaging surfaces.
 9. An interlock mechanism according to claim8, wherein each of the open arms of the U-shaped member engages with arespective one of the plurality of spring-engaging surfaces.